This application claims the priority of Korean Patent Application No. 2002-71609, filed on Nov. 18, 2002, in the Korean Intellectual Property Office, which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a microelectro mechanical system (MEMS) switch, and more particularly, to an MEMS switch that prevents switching elements from sticking and performs a stable switching operation.
2. Description of the Related Art
Radio frequency (RF) switches are a representative example of MEMS devices. RF switches are commonly used for signal routing and impedance matching in wireless communication terminals and microwave or millimeter wave band systems.
RF MEMS switches are mainly divided into capacitive switches and ohmic switches, and various types of RF MEMS switches are disclosed in U.S. Pat. No. 5,619,061.
FIG. 1 is a sectional view illustrating the structure of a conventional ohmic RF MEMS switch.
Referring to FIG. 1, spacers 2 having a predetermined height are formed at both sides of a substrate 1. The spacers 2 support conductive beams, for example, metal beam 6 located on the substrate 1. A contact plate 7 is attached to the lower surface of the beam 6 whose sides are supported by the spacers 2. A signal line 3 is formed on the substrate 1 to correspond to the contact plate 7, and RF grounds 4 are formed at both sides of the signal line 3. Insulating layers 5, formed of a dielectric material, are formed on the RF grounds 4 to prevent the beam 6 and the RF grounds 4 from directly contacting.
When a predetermined direct current (DC) voltage is applied between the beam 6 and the RF grounds 4, the beam 6 is attached to the insulating layers 5 by the electrostatic force between the beam 6 and the RF grounds 4. In this case, the contact plate 7 formed under the beam 6 contacts the signal line 3, so an RF signal passes through an electric path between the beam 6 and the signal line 3.
FIG. 2 is a sectional view illustrating the structure of a conventional capacitive RF MEMS switch.
The conventional capacitive RF MEMS switch shown in FIG. 2 operates according to an electrostatic force between a signal line 3a and a beam 6a. Here, an insulating layer 5a is formed under the beam 6a in order to prevent the loss of electrostatic force due to the direct contact between the signal line 3a and the beam 6a. 
When a predetermined DC voltage is applied between the signal line 3a and the beam 6a, the beam 6a contacts the upper surface of the signal line 3a due to the electrostatic force between the signal line 3a and the beam 6a. Accordingly, a capacitance between the beam 6a and the signal line 3a is largely increased so that the beam 6a and the signal line 3a reach an “ON” state. Here, since the insulating layer 5a, which prevents an electric short, is located between the beam 6a and the signal line 3a, the beam 6a and the signal line 3a maintain the “ON” state as long as the DC voltage is applied between the beam 6a and the signal line 3a. Thus, RF signals passes through the beam 6a and the signal line 3a. An RF blocking filter, such as a resistor or a chalk, is arranged in a DC power source, which generates a switching operation, in order to prevent the input of the RF signals. In addition, a DC blocking unit, such as a capacitor, is arranged in the RF signal path in order to prevent the input of the DC voltage from the DC power source.
The signal lines and the beams of the above-described switches contact each other as shown in FIG. 1. However, if the signal line and the beam do not completely contact each other by some reasons, the switching operation becomes unstable due to the unstable physical contact between the signal line and the beam. Thus, the beam should be formed parallel with the substrate or the surface of the signal line.
Referring to FIG. 3, in the case where two separate signal lines 3b electrically connect a beam 6b, if the beam 6b is not parallel with a substrate 1 or the signal lines 3b, the switching operation becomes unstable or the switching operation fails.
The conventional RF MEMS switch is manufactured by forming an RF blocking element, signal lines, and insulating layers using layer formation processes and etching processes. In addition, the RF MEMS switch is manufactured by forming a sacrificial layer, forming a structural layer, and then removing the sacrificial layer. The signal lines are formed by performing a photolithography process and an etching process, such as dry or wet etching. Since the signal lines are near from a moving structure, i.e., the beam, located above the signal lines, the beam and the signal lines may be stuck together due to an etchant, which is used to form the RF MEMS switch.